ABSTRACTS:

TITLE: MEASUREMENT OF GENETIC STRUCTURE WITHIN POPULATIONS USING MORAN'S SPATIAL AUTOCORRELATION STATISTICS
AUTHOR: B.K. EPPERSON AND T. LI
JOURNAL: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCE, U S A 1996 Sep 17;93(19):10528-32
ABSTRACT: The position of genetic material within chromosomes and the structure of genetic variation within populations, an important interacting influence on evolutionary and ecological processes, can be analyzed in detail by using spatial autocorrelation statistics. This paper explains the statistical properties of spatial autocorrelation statistics in and develops estimators of gene spread based on data on standing patterns of genetic variation.

Large numbers of computer simulations and a wide variety of sampling strategies are utilized. The results show that spatial autocorrelation statistics are highly predictable and informative. Thus, strong hypothesis tests for various theories can be formulated. Most strikingly, strong estimators of gene dispersal can be obtained with practical sample sizes. Details about optimal sampling strategies are also described.

KEY WORDS/PHRASES
GENE SPREAD
GENETIC VARIATION
SAMPLING STRATEGIES
SPATIAL AUTOCORRELATION STATISTICS.

TITLE: DIVERSITY AND DEPTH-SPECIFIC DISTRIBUTION OF SAR11 CLUSTER rRNA GENES FROM MARINE PLANKTONIC BACTERIA
AUTHOR: K.G. FIELD, D. GORDON, T. WRIGHT, M. RAPPE, E. URBACK, K. VERGIN, S.J. GIOVANNONI
JOURNAL: APPLIED ENVIRONMENTAL MICROBIOLOGY 1997 Jan;63(1):63-70
ABSTRACT: Small-subunit (SSU) ribosomal DNA (rDNA) gene clusters are phylogenetically related sets of SSU rRNA genes, commonly found in genes from natural populations. Genetic variability in gene clusters could result from artifacts (polymerase error or PCR chimera formation), microevolution (variation among copies within strains), or macroevolution (genetic divergence correlated with long-term evolutionary divergence).

To better understand gene clusters, this study assessed genetic diversity and distribution of a single environmental SSU rDNA gene cluster, the SAR11 cluster. SAR11 cluster genes, from a group of a class of Proteobacteria, have been recovered from coastal and midoceanic waters of the North Atlantic and Pacific. 23 new SAR11 cluster 16S rRNA genes, from 80 and 250 m in the Sargasso Sea and from surface coastal waters of the Atlantic and Pacific, were cloned, sequenced and then analyzed with previously published sequences.

Two SAR11 genes were obviously PCR chimeras, but the biological (nonchimeric) origins of most subgroups within the cluster were confirmed by checking these against separate gene libraries. Using special probes, profiles of nucleic acids were analyzed, targeting both amplified rDNAs and RNAs. Two subgroups within the SAR11 cluster showed different distributions. Some of the genetic diversity within the SAR11 gene cluster represents macroevolutionary divergence correlated with niche specialization. This demonstrates the utility for marine microbial ecology of genetic probes based on gene sequences amplified from natural populations and shows that a detailed knowledge of sequence variability may be needed to effectively design these probes.

KEY WORDS/PHRASES
CHIMERAS
EVOLUTIONARY DIVERGENCE
GENE LIBRARIES
GENETIC PROBES
NICHE SPECIALIZATION
PHYLOGENETICALLY RELATED
rRNA GENES
SMALL-SUBUNIT (SSU)
RIBOSOMAL DNA (rDNA)
GENE CLUSTERS

TITLE: A MOLECULAR PHYLOGENY OF MOBILE RIVER DRAINAGE BASIN PLEUROCERID SNAILS (CAENOGASTROPODA: CERITHIOIDEA)
AUTHOR: C. LYDEARD, W.E. HOLZNAGEL, J. GARNER, P. HARTFIELD AND J.M.PIERSON
JOURNAL: MOLECULAR PHYLOGENETIC EVOLUTION 1997 Feb;7(1):117-28
ABSTRACT: Gene analysis may demonstrate evolutionary and taxonomical relationships that are not evidence from physical appearance. Sequences from the mitochondrial 16S rRNA gene were obtained to construct a molecular phylogenic history for Mobile River drainage basin snails. Data from 876 aligned positions generated a single most-simple tree for each of three analytical approaches: (1) equal weighting, (2) transversions weighted 2 x transitions; and (3) transversions weighted 4 x transitions. The resulting trees depict the genera Elimia and Pleurocera as sister taxa.

When transversions were weighted 10x transitions a single most-simple tree was obtained with the only topological difference being L. picta depicted as sister to L. taeniata and L. ampla and L. plicata is now the most basal pleurocerid examined. Many of the Elimia species are closely related, but further data is needed before making any taxonomic recommendations. L. picta and L. plicata are quite distinct from each other and all other pleurocerid species examined. These data serve as an important foundation for future studies examining conservation genetics and systematics of this diverse and imperiled family of snails.

KEY WORDS/PHRASES
ALIGNED POSITIONS
CONSERVATION GENETICS
MITOCHONDRIAL RRNA GENE
PHYLOGENIC HISTORY